Gas tube amplifier



c- 93 a. JOBST ET AL 1,389,749

GAS TUBE AMPLIFIER Fi l ed Jan. 24. 1931 INVENTORS GUNTHER JOBST JOHANNES RICHTER BY W L A WEHNERT Patented Dec. 6, 1932 UNITED STATES PATENT OFFICE G'll'NTEER JOBST, J'OHANNES RICHTER, AND WALIDEMAR WEHNERT, OF BERLIN, GER- MANY, ASSIGNORS TO TELEFUNKEN GESELLSCHAFT FUR DRAHTLOSE TELEGBAPHIE M. B. 5., OF BERLIN, GERMANY, A CORPORATION OF GERMANY GAS TUBE AMPLIFIER Application filed January 24, 1931, Serial No. 511,0395, and in Germany January 7, 1980.

Application for this invention filed in Germany January 7, 1930.

The present invention relates to gas tube amplifiers, and more particularly to a method of eliminating hum in line-supplied radio receiver sets.

The single figure of the drawing illustrates a system comprising a plurality of gas tube amplifiers connected in cascade in accordance with the present invention.

In the case of gas-filled amplifier tubes in which the control action is secured by virtue of an external electrode, it has been discovered that the amplifier effect is markedly dependent upon the frequency of the alternating current to be amplified. Thus, for gasfilled external control tubes the audio amplification is extremely low compared with the amplification of radio currents.

This fact may be accounted for in some such manner as this: The positive gas ionic current and the electronic current tend to compensate, by charging up the tube walls, the controlling field of the external electrode in the presence of audio oscillation processes, while for rapid alternating current potentials a compensation, or neutralization, of the control' action of the exterior electrode does not occur owing to the greater inertia of the ions. On the contrary, the electronic current which now predominates will impart a negative charge to the inner walls of the tube, and this negative charge exercises the identical effect as a grid biasing potential. Hence, the pressure prevailing inside the tube can be so chosen that maximum amplification of the tube will be obtained for superaudible frequency ranges, while the ion mobility and the dimensions of the tube are chosen so large that audio amplification is very low.

This aforementioned characteristic makes I theluse of gas-filled external-control tubes in line-supplied receiver sets comprising tubes directly heated from an alternating current net-work extremely advantageous, in view of the fact that mixing of the power line hum, as a 50-cycle hum, and the output potential is precluded from the outset.

Another characteristic of gas-filled tubes is that radio frequency energy modulated with audio frequency is so rectified and amplified that the degree of amplification decreases as the modulation frequency grows. Thus, the use of gas-filled external control tubes in this way results in reproduction in a full and deep timber contradistinct from what is the rule in the usual type of broadcast receiver sets where just the low pitches are generally reproduced defectively. This is also of great advantage in the case of bat tery-supplied receiver sets.

It is, therefore, suitable for the foregoing reasons to employ external control tubes primarily in the first stages of the receiver. That is to say, it is advantageous to use tubes filled with an inert gas such as helium, argon, hydrogen, i. e., gases exhibiting a relatively constant pressure for continuous electric discharges occurring between 10 and 10' millimeters, Hg column. It is, also, possible to fill the tube with mercury vapor which by means of a certain supply, or quantity, of mercury kept inside the vessel is maintained at a constant mercury vapor pressure, where as the partial pressure of other gases, primarily oxygen, must be kept as low as possible. The value of the pressure to be employed is a function both of the nature of the gas to be used as well as the geometry of the tube.

Particularly suitable in the sense of the present disclosure are gas-filled external-control tubes comprising electrodes so disposed inside the tube envelope that the direction of electronic discharge will occur substantially at right angles to the longitudinal axis of the tube, while the distance between the heated filament, or'some parts thereof, and the most proximate part of the envelope wall is smaller than the distance between filament and anode. This could be attained, for example, by discharge tubes having a cross-sectional form other than circular, e. g., a flattened form, or an elongated form. Owing to the geometrical disposition of the electrodes in reference to one another, discharge tubes of this kind insure particularly high amplification.

What we claim is 1. In combination, in a radio receiver, a.- tunable radio frequency amplifier stage ineluding a tube having its electrodes arranged for energization from a source of alternating current, a source of radio frequency energy to be amplified, said tube being provided with an external control electrode coupled to said source, an atmosphere of gas within the tube, the relation between the geometry of the tube and the gas pressure being such that radio frequencies are amplified more efliciently than audible frequencies, a detector stage including a tunable input circuit coupled to the amplifier output, said detector including a tube of the same construction as said first tube whereby hum frequencies due to said alternating current are poorly amplified.

2. In combination, in a radio receiver, a tunable radio frequency amplifier stage including a tube having its electrodes arranged for energization from a source of alternating current, a source of radio frequency energy to be amplified, said tube being provided with an external control electrode coupled to said source, an atmosphere of gas within the tube, the relation between the geometry of the tube and the gas pressure being such that radio frequencies are amplified more efficiently than audible frequencies, a detector stage including a tunable input circuit coupled to the amplifier output, said detector including a tube of the same construction as said first tube whereby hum frequencies due to said alternating current are poorly amplified, an audio frequency amplifier, having its input circuit resistively coupled to said detector output, including a tube of the'same construction as said first two tubes, and means for applying a positive potential to the external control elebctrode of the audio frequency amplifier tu e.

3. In combination, in a radio receiver, a detector stage having a tunable input circuit and including a tube of the type having an external grid whereby the grid to cathode capacity of the tube is low, an audio frequency amplifier stage including a tube of the same type, a. resistor having one side connected in common to the anode of the detector tube and the external grid of the amplifier tube-,means for connecting the other side of the resistor to a source of positive potential, and both said tubes being filled with an inert gas whose pressure is related in a predetermined manner tt audio frequency amplification.

GUNTHER J OBST. J OHANNES RICHTER. WALDEMAR WEHNERT. 

